1. Field of the Invention
This invention relates generally to screw fasteners, and, more particularly, to captive screw assemblies suitable for mounting in flat panels.
2. Description of the Prior Art
Captive screw assemblies are commonly used in the aerospace industry to secure removable panels to aircraft frames or assemblies, and to mount a variety of detachable devices on aircraft panels. Such assemblies are particularly well suited to applications in which the panel is repeatedly opened and closed for servicing or inspection, or in which components are alternatively mounted or dismounted on a panel.
The thin and fairly soft aluminum of most aircraft panels renders them generally unsuitable for repeated threading and unthreading of hardened screws. Consequently, steel housings typically are permanently affixed to an aircraft panel for mounting such screws. Once installed, these housings can retain the screws, even while a screw is not engaged in a threaded bore of a receiving nut. Accordingly, these screws are described as being "captive."
A typical screw housing is fitted into an aperture in a panel. To secure the housing in the panel, the diameter of the housing is matched to the diameter of the aperture and the length of the housing is appropriate to the thickness of the panel. However, because different aircraft panels have different thicknesses, the aircraft manufacturer or maintenance facility must stock a large and costly inventory of captive screws and their housings.
In addition, while captive screw assemblies are generally convenient and easy to use after they are installed, the initial installation of a captive screw assembly can be complex and time consuming. In many instances, the diameter of the panel aperture must be adapted to that of the screw housing, and the installation can require a series of operations on both sides of the panel. For example, a portion of the housing can be inserted from one side of the panel and fastened to the panel from the other side, in a two-step operation requiring an elaborate assembly tool or the cooperation of two assemblers.
Accordingly, there is a need for a captive screw assembly that is sized for a range of panel thicknesses, thereby reducing the variety and number of captive screw assemblies needed by an aircraft manufacturer or maintenance facility. Further, it should be appreciated that there is also a need for a captive screw assembly that can be installed in a variety of panels with minimal panel preparation. The present invention fulfills these needs.